hacking-network.h

/* This function accepts a socket FD and a ptr to the null terminated
 * string to send.  The function will make sure all the bytes of the
 * string are sent.  Returns 1 on success and 0 on failure.
 */
int send_string(int sockfd, unsigned char *buffer) {
   int sent_bytes, bytes_to_send;
   bytes_to_send = strlen(buffer);
   while(bytes_to_send > 0) {
      sent_bytes = send(sockfd, buffer, bytes_to_send, 0);
      if(sent_bytes == -1)
         return 0; // return 0 on send error
      bytes_to_send -= sent_bytes;
      buffer += sent_bytes;
   }
   return 1; // return 1 on success
}

/* This function accepts a socket FD and a ptr to a destination
 * buffer.  It will receive from the socket until the EOL byte
 * sequence in seen.  The EOL bytes are read from the socket, but
 * the destination buffer is terminated before these bytes.
 * Returns the size of the read line (without EOL bytes).
 */
int recv_line(int sockfd, unsigned char *dest_buffer) {
#define EOL "\r\n" // End-Of-Line byte sequence
#define EOL_SIZE 2
   unsigned char *ptr;
   int eol_matched = 0;

   ptr = dest_buffer;
   while(recv(sockfd, ptr, 1, 0) == 1) { // read a single byte
      if(*ptr == EOL[eol_matched]) { // does this byte match terminator
         eol_matched++;
         if(eol_matched == EOL_SIZE) { // if all bytes match terminator,
            *(ptr+1-EOL_SIZE) = '\0'; // terminate the string
            return strlen(dest_buffer); // return bytes recevied
         }
      } else {
         eol_matched = 0;
      }   
      ptr++; // increment the pointer to the next byter;
   }
   return 0; // didn't find the end of line characters
}


/* Structure for Ethernet headers */
#define ETHER_ADDR_LEN 6
#define ETHER_HDR_LEN 14

struct ether_hdr {
   unsigned char ether_dest_addr[ETHER_ADDR_LEN]; // Destination MAC address
   unsigned char ether_src_addr[ETHER_ADDR_LEN];  // Source MAC address
   unsigned short ether_type; // Type of Ethernet packet
};

/* Structure for Internet Protocol (IP) headers */
struct ip_hdr {
   unsigned char ip_version_and_header_length; // version and header length combined
   unsigned char ip_tos;          // type of service
   unsigned short ip_len;         // total length
   unsigned short ip_id;          // identification number
   unsigned short ip_frag_offset; // fragment offset and flags
   unsigned char ip_ttl;          // time to live
   unsigned char ip_type;         // protocol type
   unsigned short ip_checksum;    // checksum
   unsigned int ip_src_addr;      // source IP address
   unsigned int ip_dest_addr;     // destination IP address
};

/* Structure for Transmission Control Protocol (TCP) headers */
struct tcp_hdr {
   unsigned short tcp_src_port;   // source TCP port
   unsigned short tcp_dest_port;  // destination TCP port
   unsigned int tcp_seq;          // TCP sequence number
   unsigned int tcp_ack;          // TCP acknowledgement number
   unsigned char reserved:4;      // 4-bits from the 6-bits of reserved space
   unsigned char tcp_offset:4;    // TCP data offset for little endian host
   unsigned char tcp_flags;       // TCP flags (and 2-bits from reserved space)
#define TCP_FIN   0x01
#define TCP_SYN   0x02
#define TCP_RST   0x04
#define TCP_PUSH  0x08
#define TCP_ACK   0x10
#define TCP_URG   0x20
   unsigned short tcp_window;     // TCP window size
   unsigned short tcp_checksum;   // TCP checksum
   unsigned short tcp_urgent;     // TCP urgent pointer
};